Megalonyx jeffersonii
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Megalonyx Temporal range: late Miocene to , 10.3–0.011 Ma |
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| M. wheatleyi skeleton. | |
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| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Superorder: | Xenarthra |
| Order: | Pilosa |
| Family: |
Megalonychidae Gervais, 1855 |
| Subfamily: | Megalonychinae |
| Genus: |
†Megalonyx Harlan, 1825 |
| Species | |
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Megalonyx (Greek, "large claw") is an extinct genus of ground sloths of the family Megalonychidae endemic to North America from the Hemphillian of the Late Miocene through to the Rancholabrean of the , living from ~10.3 Mya—11,000 years ago, existing for approximately 10.289 million years. Type species, M. jeffersonii, measured about 3 m (9.8 ft) and weighed up to 1,000 kilograms.
Megalonyx was a large, heavily built animal about 3 m (9.8 ft) long. Its maximum weight is estimated at 1,000 kg (2,205 lb). This is medium-sized among the giant ground sloths. Like other ground sloths it had a blunt snout, massive jaw, and large peg-like teeth. The hind limbs were plantigrade (flat-footed) and this, along with its stout tail, allowed it to rear up into a semi-erect position to feed on tree leaves. The forelimbs had three highly developed claws that were probably used to strip leaves and tear off branches.
Ongoing excavations at Tarkio Valley in southwest Iowa may reveal something of the familial life of Megalonyx. An adult was found in direct association with two juveniles of different ages, suggesting that adults cared for young of different generations.
Megalonyx ranged over much of North and Central America. Their remains have been found as far north as Alaska and the Yukon.
M. jeffersonii was apparently the most wide ranging giant ground sloth. Fossils are known from many Pleistocene sites in the United States, including most of the states east of the Rocky Mountains as well as along the west coast. It was the only ground sloth to range as far north as the present-day Yukon and Alaska.
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